This invention relates to ink jet printer maintenance systems and more particularly to a droplet sensing and recovery system for a full width array printhead, wherein each nozzle is checked for failure of droplet ejection or misdirectionality of ejected droplet and recovery hardware is used to return the faulty nozzle detected to proper operation.
A continuing problem with thermal ink jet printers is the drying of ink at the printhead nozzles, thus causing clogging or partially blocking the nozzles. The result of clogged nozzles is that droplets fail to be ejected or that droplets fail to follow the desired droplet trajectory to the recording medium. To overcome this, a maintenance station is commonly used whereby the printhead is capped or sealed in a high humidity environment to prevent or to greatly retard drying. Maintenance stations include the capability of exerting a vacuum to suck ink from the nozzles to clear the nozzles of dried ink or viscous plugs and to remove any air bubbles that may have accumulated or formed in the printhead. This sucking of ink by the maintenance station is generally referenced to as priming. Periodic ejection of ink droplets from the nozzles while the printhead is at the maintenance station also clears the nozzles of dried ink and viscous plugs of ink.
Full width array printheads having 300 to 600 nozzles per inch or more present unique problems for maintenance because of the large numbers of nozzles. For example, a 12 inch wide printhead having 600 nozzles per inch would employ 7200 nozzles, each of which is susceptible of drying out. It is not economically practical to re-prime all of the nozzles each time a few may become clogged, for too much ink is wasted. Many approaches have been undertaken by the prior art to maintain the operability of all of the nozzles in a full width array printhead, but none have interrogated each nozzle to detect droplet ejection and droplet directionality and address only those malfunctioning nozzles with recovery hardware, thereby conserving the consumption of ink.
U.S. Pat. No. 5,250,962 to Fisher et al. discloses a movable priming station capable of priming a portion of an extended array of nozzles at one time in an ink jet printhead by applying a vacuum to at least one nozzle located in the array. The movable priming station includes a support which is moved along the length of the nozzle array and a vacuum tube is attached to the support. One end of the tube functions as a vacuum port which confronts but is spaced from the nozzles, when the support is moved laterally along the nozzle array.
U.S. Pat. No. 5,117,244 to Yu discloses a device to cap a full width array, thermal ink jet printhead without the need of moving the printhead or the paper transport. The capping device has a resilient gasket which contains magnetic material and is attached to the printhead by a relatively thin flexible boot or sleeve. The paper transport is a belt adjacently spaced parallel to the face of the printhead containing the nozzle array. The transport belt is flat and has a steel bar disposed in sliding contact beneath the belt portion confronting the printhead. During operation of the printer, an electromagnet disposed on the printhead is energized, allowing the steel bar to attract the magnetic gasket and seal the gasket to the transport belt.
U.S. Pat. No. 5,304,814 to Markham discloses a sensor circuit and method for detecting the presence of an ink droplet ejected from an ink jet printhead. An integrator integrates the output of the sensor and a high gain amplifier amplifies the integrated signal to provide a sensor circuit output signal. When the droplet at least partially interrupts the light path, the integrated output signal indicates the presence or passage of the droplet. The circuit is preferably used to control a heating element of a thermal ink jet printhead by adjusting the power to the heating elements to assure its operation with a power adequate to eject a droplet.